The present invention relates generally to non-impact page printers and, more particularly, to a method for increasing the grayscale resolution of a non-impact, light emitting diode type page printer.
The tremendous growth in the computer industry has resulted in a corresponding growth in computer peripherals, particularly low cost desk top page printers, which are used to provide a paper or hard copy of the output from a computer. Such printers may be employed for desk top publishing, typeset proofing, normal business or home printing or in any other field where low cost, high quality images are required. As computer speeds increased, it became apparent that traditional impact-type printers were not able to operate at the speeds required to keep up with the computer. Some printers utilize a buffer system to receive and temporarily hold the information from the computer to be printed until such time as the impact-type printer could "catch up" and print all of the information. As an alternative, a variety of non-impact printers were developed. The technologies involved in such non-impact printers include laser printers, ink jet printers and light emitting diode (LED) printers, as well as a variety of other less well known printer technologies. All of these technologies are capable of operating at speeds which are generally higher than the speeds attainable by impact-type printers.
A typical non-impact page printer which employs LED technology operates by lighting a series of LEDs, generally along a single row for a short time, in accordance with a prescribed pattern, in order to produce one line of charge comprising a series of small sized dots on an image drum which, in turn, imposes the dots on a sheet of paper within the printer. The pattern of the dots is carefully controlled so that as the image drum and the paper move and the LEDs are lit or flashed a plurality of times, the dots eventually form printed images which generally include characters, such as alphanumeric characters. A typical LED type non-impact page printer is capable of placing dots on the moving page at a resolution of about 300 dots per inch in either the vertical or the horizontal direction, or approximately 90,000 dots per square inch of paper. Printers of this type are typically referred to as dot matrix printers and are generally well known in the art and commercially available from a variety of manufacturers, including Okidata, the assignee of the present application.
While non-impact LED page printers of the type described above are well suited for the printing of many images, including standard alphanumeric characters of a type which would typically be used in conjunction with the printing of textual material, such as letters, brochures, etc., as well as many other applications, such printers are not particularly well suited to printing applications which require a high degree of grayscale resolution to maintain good quality. Quality appears poor when the eye can notice the staircase on the periphery of an alphanumeric character or the individual component dots in a shade of gray and appears to be good when these components cannot be resolved. Such applications include printing, photographs, some graphical materials and the like.
The present invention relates to a method of increasing the grayscale resolution of a non-impact LED type page printer to a level which permits the printing of good quality images utilizing standard, state-of-the-art equipment. The method of the present invention can be easily employed for the purpose of retrofitting existing LED page printers to provide such increased resolution and good quality images at a relatively low cost.